Pulse Oximeter and CO-oximeters

In the event of carbon monoxide poisoning, pulse oximeters are unable to detect any abnormalities in the oxygenation status of a patient. Because of this, a pulse co-oximeter would be necessary to delineate the actual gas components of the blood.

Carboxyhemoglobin

Normally, carbon monoxide (CO) can be found in small amounts in the atmosphere. But due to pollution and burning of fossil fuels, the air will contain significant quantities of CO. When inhaled (such as getting trapped inside burning structures, or tobacco smoking), CO will accumulate in lethal amounts. Carbon monoxide will bind with hemoglobin component of the red blood cell to form carboxyhemoglobin. Compared to O₂, CO has a higher affinity to hemoglobin which means hemoglobin would prefer binding with CO. Consequently, there wouldn’t be enough oxygen to be delivered to the body cells and the person might suffer from severe hypoxia which could eventually lead to death.

The fact that pulse oximeters are isolated to one type of hemoglobin gives a lot of advantages for pulse co-oximeters. The former only uses two wavelengths of light that could not differentiate carboxyhemoglobin from oxyhemoglobin. Hence, with a pulse oximeter, the SpO₂ of a person would remain normal despite low oxygen levels.

On the other hand, pulse CO-oximeter is a telemetry unit that analyzes multiple wavelengths of light to accurately measure the total amount of hemoglobin including oxyhemoglobin, carboxyhemoglobin, methemoglobin, reduced hemoglobin, and total hemoglobin. It yields fast and reliable results that facilitate timely diagnosis and counseling with the physician. Pulse CO-oximeters utilize all 7 wavelengths to acquire and quantify data on blood constituents. Certain models can also read through the tissues during motion and low perfusion.

Pulse oximetry and CO-oximetry are not tests, but a methodology. They do not generate all the information required to determine the total respiratory status. They cannot be a substitute for arterial blood gas and other tests for respiratory function. However, they may be used for monitoring and early identification of signs of hypoxia and certain cardiopulmonary problems.